RATIONALE: Drugs used in chemotherapy, such as etoposide, methylprednisolone, cytarabine, and cisplatin, work in different ways to stop the growth of cancer cells, either by killing the cells or by stopping them from dividing. Monoclonal antibodies, such as rituximab and yttrium Y 90 ibritumomab tiuxetan, can block cancer growth in different ways. Some block the ability of cancer cells to grow and spread. Others find cancer cells and help kill them or carry cancer-killing substances to them without harming normal cells. Giving more than one drug (combination chemotherapy) together with rituximab and yttrium Y 90 ibritumomab tiuxetan may kill more cancer cells.